﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!!!");
            Double dd = 3.14;
            Double sum;
            Console.WriteLine("请输入圆的半径");
            Double d = Double.Parse(Console.ReadLine());
            sum = d * d * (3.14);
            Console.WriteLine(sum);
        }
    }
}
